diff --git a/scripts/ashtakavarga.py b/scripts/ashtakavarga.py
index 8d71a019..95694eae 100644
--- a/scripts/ashtakavarga.py
+++ b/scripts/ashtakavarga.py
@@ -586,3 +586,37 @@ def calc_sodhita_av(bav_results: Dict, planets: Dict, asc_sign_idx: int) -> Dict
         'reduction_summary': total_reduction,
         'validation_note': 'Sodhita AV ≤ 原始BAV（逐宫位）',
     }
+
+
+TRIKONA_SIGN_GROUPS = (
+    (0, 4, 8),   # Aries, Leo, Sagittarius
+    (1, 5, 9),   # Taurus, Virgo, Capricorn
+    (2, 6, 10),  # Gemini, Libra, Aquarius
+    (3, 7, 11),  # Cancer, Scorpio, Pisces
+)
+
+
+def calc_trikona_shodhana(sav_scores: List[int]) -> Dict:
+    """Apply the classical Trikona Shodhana reduction to a 12-sign SAV row.
+
+    The minimum value in each elemental trine is removed from all three signs;
+    the original row remains in the result for auditability.
+    """
+    if len(sav_scores) != 12:
+        raise ValueError('SAV scores must contain exactly 12 signs')
+    original = [int(value) for value in sav_scores]
+    reduced = original[:]
+    groups = []
+    for indexes in TRIKONA_SIGN_GROUPS:
+        baseline = min(original[index] for index in indexes)
+        for index in indexes:
+            reduced[index] -= baseline
+        groups.append({'sign_indexes': list(indexes), 'baseline_removed': baseline})
+    return {
+        'method': 'Trikona Shodhana',
+        'original_scores': original,
+        'reduced_scores': reduced,
+        'trikona_groups': groups,
+        'status': 'executed',
+        'claim_boundary': 'Standalone classical reduction; Ekadhipatya Shodhana remains a separate layer.',
+    }
diff --git a/tests/test_trikona_shodhana.py b/tests/test_trikona_shodhana.py
new file mode 100644
index 00000000..9dc50b0d
--- /dev/null
+++ b/tests/test_trikona_shodhana.py
@@ -0,0 +1,14 @@
+import sys
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT / 'scripts'))
+
+from ashtakavarga import calc_trikona_shodhana  # noqa: E402
+
+
+def test_trikona_shodhana_removes_each_trine_baseline() -> None:
+    result = calc_trikona_shodhana(list(range(1, 13)))
+    assert result['reduced_scores'] == [0, 0, 0, 0, 4, 4, 4, 4, 8, 8, 8, 8]
+    assert result['trikona_groups'][0]['baseline_removed'] == 1